Plastic fasteners (also commonly referred to in the art as plastic attachments) are well known in the art and commonly used to couple articles of commerce to packaging, buttons to fabric, merchandising tags to articles of commerce, or, in general, any two desired articles. One type of plastic fastener which is widely used in commerce is manufactured in an H-shaped configuration, with two shortened parallel cross-bars, or T-bars, interconnected at their approximate midpoints by a thin, flexible filament that extends orthogonally therebetween.
Plastic fasteners of the type described above are commonly fabricated as part of continuously connected fastener stock that is produced from one or more flexible plastic materials, such as nylon and polypropylene, using conventional molding or stamping techniques. Referring now to FIG. 1, there is shown a length of continuously connected fastener stock 11 that is well known in the art. Fastener stock 11 is formed from two elongated and continuous plastic side members, or rails, 13 and 15 that are interconnected by a plurality of equidistantly spaced cross-links, or filaments, 17. Due its ladder-like appearance, fastener stock 11 is also commonly referred to as ladder-type fastener stock, or ladder stock, in the art.
By severing each of side rails 13 and 15 at the approximate midpoint between successive filaments 17, a plurality of individual plastic fasteners 18 can be produced from ladder stock 11. Each plastic fastener 18 produced from ladder stock 11 comprises a pair of cross-bars 19 and 21 that are interconnected by a thin, flexible filament 23, with cross-bars 19 and 21 being derived from side rails 13 and 15, respectively, and filament 23 being derived from a corresponding cross-link 17. Ladder stock of the type described above is shown in U.S. Pat. No. 4,039,078 to A. R. Bone and U.S. Pat. No. 5,615,816 to C. L. Deschenes, the disclosures of both patents being incorporated herein by reference.
Ladder stock of the type described above is presently manufactured and sold by Avery Dennison™ Corporation of Pasadena, Calif. under the Plastic Staple® and Elastic Staple™ lines of plastic fasteners. The commercialized ladder stock is traditionally wound onto a reel, or spool, which is sized and shaped to hold a supply of ladder stock that yields approximately 25,000 fasteners.
Either manually or with the aid of specifically designed devices, individual fasteners are commonly severed from a supply of ladder stock and, in turn, dispensed in order to secure together two or more items. For example, in commonly assigned U.S. Pat. No. 7,036,680 to Steven E. Flannery, which is incorporated herein by reference, there is disclosed a pneumatically driven device for dispensing individual plastic fasteners from a reel of continuously connected ladder stock. The device includes a protective outer housing and a pair of hollow slotted needles that protrude out from one end of the housing in a parallel relationship, each needle having a rear end, a longitudinal bore and a sharpened tip adapted to penetrate through the items to be fastened. The device also includes a feed mechanism that relies upon a pair of rotatable feed wheels to engage selected cross-links of the ladder stock so as to advance the side rails into direct axial alignment behind the longitudinal bores defined by the pair of needles. With each side rail positioned directly behind a corresponding needle, a pair of articulating sharpened knife blades is actuated so as to cut the side rails of the ladder stock at the approximate midpoint between successive cross-links and thereby separate an individual plastic fastener from the remainder of the ladder stock. The device further includes an ejection mechanism disposed within the interior cavity of the housing that ejects the cross-bars of the severed fastener out through the pair of hollowed needles and, in turn, through the intended items. The ejection mechanism includes an ejector rod slide, or carriage, that is pneumatically driven by a single air cylinder to travel back and forth within the protective housing. The ejector rod slide supports a pair of parallel ejector rods, each ejector rod being dimensioned and positioned to selectively penetrate through a corresponding needle in order to eject an associated cross-bar of the severed fastener out therefrom.
As noted briefly above, fasteners of the type as described above are commonly used in a wide variety of different applications to secure together two or more items. For example, fasteners of the type described above are commonly used in packaging applications to secure an article of commerce to a display card. As part of the attachment process, the display card is first positioned on an anvil for the fastener dispensing machine. Next, the article of commerce is placed in its desired location on the display card. The machine is then downwardly displaced until the pair of needles penetrates through the display card on opposite sides of the article of commerce and in close proximity relative thereto. As a fastener is severed from the fastener stock and subsequently ejected through the hollow needles, each of the pair of cross-members engages the underside of the card with the thin filament stretching tightly across the front of the article. In this capacity, the dispensed fastener serves to secure the article to the display card in an inconspicuous and unobtrusive manner.
In certain applications, it has been found to be desirable to modify the spacing between the pair of needles for fastener dispensing devices of the type described above. For instance, adjusting the spacing between needles is often required to accommodate supplies of ladder stock with cross-links of varying lengths (e.g., between 0.25 inches and 0.38 inches). In addition, adjusting the spacing between needles is often required to account for variances in the size and shape of articles that are commonly joined using plastic fasteners (e.g., items of different widths that are secured to display cards).
Accordingly, fastener dispensing devices with variable needle spacing are known in the art and are commonly referred to as variable needle system (VNS) devices or VNS modules. One well known type of VNS device includes a pair of needle mounts, or blocks, each of which is shaped to include a bore dimensioned to fittingly receive a corresponding needle. As part of its design, one needle block for the VNS device is held fixed in place and the other needle block is mounted on a laterally disposed axle and is thereby capable of displacement towards and/or away from the fixed needle block through rotation of a spacing wheel. In this manner, the spacing between the pair of needle blocks and, in turn, the needles mounted thereon, can be adjusted through rotation of the spacing wheel.
Although well known in the art, fastener dispensing devices with variable needle spacing capabilities typically suffer from a few notable shortcomings.
As a first shortcoming, fastener dispensing devices of the type described above are traditionally constructed as self-contained, modular units. As a result, the spacing range between needles is generally limited by the length of the axle on which the movable needle block is mounted and, more generally, by the overall width of the VNS module housing. As can be appreciated, it has been found that this restriction on the maximum spacing between needles precludes use of traditional VNS devices in certain larger-scale packaging applications (e.g., in securing larger sized objects to display cards), which is highly undesirable.
As a second shortcoming, fastener dispensing devices of the type described above exert a significant amount of stress on each fastener during the ejection process which, in turn, can lead to inadvertent breakage of the fastener, which is highly undesirable. Specifically, it has been found that as each cross-bar is ejected, the fastener is temporarily stretched to the extent necessary so that the cross-bar can exit out through the tip of its corresponding needle. Once each cross-bar exits its corresponding needle, the temporary stretching force applied to the fastener by the ejector rods and the stress resulting therefrom is withdrawn. However, because traditional fastener dispensing devices are designed to simultaneously eject both cross-bars of the same fastener through their corresponding needles (i.e., with the cross-bars ejected in phase with one another), the cumulative effect of the temporary stress applied to the fastener often results in fastener breakage during the ejection process.
As a third shortcoming, fastener dispensing devices of the type described above include a feed mechanism that engages one or more cross-links in order to advance the ladder stock into position for severing of the lowermost fastener. However, it is to be understood that the feed mechanism typically engages cross-links that are significantly behind the lowermost cross-link (i.e., the cross-link for the fastener to be separated from the remainder of the ladder stock). As a consequence, a considerable amount of misalignment, or drift, of the lowermost cross-links within the device is experienced prior to the side rail cutting process. Ladder stock drift in turn causes the device to cut each side rail at a location away from the exact midpoint between successive fasteners, thereby resulting in fasteners that fail to have the optimal H-shaped configuration. In response thereto, a considerable degree of user adjustment is often required in order to maintain accurate and consistent cutting of side rails, which is both labor-intensive and often unreliable.
As a fourth shortcoming, fastener dispensing devices of the type described above utilize a relatively complex locking mechanism to releasably retain each sharpened needle within its corresponding needle block. Specifically, as noted briefly above, each needle is fittingly inserted into a bore formed into its corresponding needle block. To secure each needle within its corresponding bore, a needle lock screw is ratably driven transversely through each needle block and into selective engagement within a scallop formed in the base of its associated needle. As a consequence, it to be understood that the process for removing, repairing and/or replacing needles is not only labor-intensive and time-consuming but also requires the use of an additional tool, such as a screwdriver, which is highly undesirable.